physico-chemical characterisation of native air-formed oxide films on Al-Mg alloys at low temperature . Influence of water

摘要

Natural oxide films on two cold-rolled Al-Mgalloys were studied using several techniques (XPS, SIMS, ToF-SIMS, GDOS, SEM, TEM, Wetting measurements). The aim wasto characterise and compare the oxide layers formed on the twomaterials in order to better understand the influence of thethermomechanical history. The experimental tools used allowedthe determination of the influence of the annealing process on thenature and structure of the oxides. The hydration and Bronstedbehaviour were also investigated. The thickness of the layer, theamount of magnesium oxide and its dissolving resistance in waterare strongly modified by the annealing. The oxide film formed onthe annealed material is twice as thick as the one on the non-reheated material. The layer on the annealed material containsmore magnesium oxide and contains the crystalline forms: β-Al2O3 and bayerite (Al(OH)3). On the contrary, the oxide filmformed on the as-rolled material seems to be amorphous. Themagnesium oxide is less soluble in water in the annealed film thanin the non-reheated one. Furthermore, aluminium and andmagnesium oxides were found to be hydroxylated on both alloys,and the layer surfaces to behave like a bronsted meaning base.